Assigning minimum via number to net classes

[Norman]

Hello,

To relax reliability issues in analog designs due to maximum allowable
current densities per via, you use often arrays of vias to change
between metal layers (e.g. using 2 rows and 2 columns, thus 4 contacts,
instead of the default one contact)

Do somebody know, if it is possible to define in net classes a minimum
number of contact per via.

Or is there maybe a way to search in a design single contacts, i.e.
contacts with 1 row and 1 column?


Best regards

Norman

 

[vdvalk@rogers.com]

Norman:



The last time I investigated the routing tools, it was required that
you create single via structures for the automatic routing. Multiple
vias were not chosen by default in any way!

If you wanted a 2x2 via as the defaut, I have written code to fake out
the tool and tell it the structure had a via that was actually a 2x2
array!
(or 1x2 but that was messy!)


To increase reliability, you could write design rules to flag isolated
vias. This is trivial drc code.
(
this is easy if your definition of non-isolated vias is smaller than:
the definition of non-isolated vias OR electrically isolated vias.
if not the code involves grows (of less than 1/2 of the smallest of
these) and and-nots of conductor(s)
some drc tools now do this slightly more efficently than several years
ago!

Lets say for simplicity that VIAX is isolated if it is farther than 1u
from any other VIAX
and VIAX to VIAX spacing on different METX polygons is 1.2u

CHECK_ISO_VIAX = grow( VIAX 0.5 )
ISO_VIAX = select( CHECK_ISO_VIAX straddle VIAX number<2 ) /* this
psudo code is not valid */
)

Fixing it is another issue.

-- Gerry